1. Field of the Invention
This invention relates to an improved process and growth medium for propagating Haemophilus gallinarum, with the object of providing a practical immunizing agent for infectious coryza. Infectious coryza has long been a major disease problem for poultry flocks, and particularly for laying chicken flocks. Although infected chickens normally recover within a few weeks, the disease often is complicated by other infections, in which cases chronic respiratory disorders may persist for months, with resultant economic losses. The disease is particularly troublesome in a continuous laying operation with different age groups of birds, and with operations conducted near another flock which might transmit the disease.
Infectious coryza is an acute respiratory disease of chickens caused by Haemophilus gallinarum. The disease manifests as severe swelling of the frontal sinus, and can lead to infection of the airsac and generalized airsaculitus. Sometimes chronic secondary infections develop which necessitate culling.
2. Description of the Prior Art
Many attempts have been made to control infectious coryza through such methods as isolation rearing, yearly disposal of laying flocks, and, in some cases, complete depopulation. Such efforts have provided some benefits, but in most cases the disease has reappeared.
It was observed that chickens that had survived an attack of infectious coryza developed a resistance or immunity to reinfection. This observation led to the belief that a controlled infection with a live virulent culture of Haemophilus gallinarum administered at the proper time would produce good immunity with a minimum of losses from complicating diseases. This method is not a completely satisfactory solution to the infectious coryza problem because even when the disease is given to young birds before they reach laying age there are still losses due to culls.
More recently, attempts have been made to control infectious coryza with inactivated bacterins prepared from cultured Haemophilus gallinarum. One such bacterin is described in Avian Diseases, 5: 37-47 (1961). Egg-yolk-propagated bacterins as described therein lessened the severity and duration of infectious coryza, and provided benefits against related infections and decreased egg production. This type of bacterin has not been widely accepted because it is not completely effective in preventing egg production losses nor does it protect against certain upper respiratory signs.
Another inactivated bacterin prepared by growth of Haemophilus gallinarum in an infusion broth was described in Avian Diseases, 15, 109-117 (1971). The bacterin described therein effectively protects the upper respiratory tract of chickens from infectious coryza. However, while the bacterin prepared from infusion broth has been quite effective, it suffers from the fact that at least 10.sup.8 colony forming units per milliliter of immunogen is required for effective protection, and the bacterin required concentration by centrifugation or the like in order to provide the minimum effective concentration of 10.sup.8 CFU/ml.
A general discussion of results of inactivated bacterins for prevention of disease caused by Haemophilus gallinarum is found in Avian Diseases, 7: 239-256 (1963).
Ortiz and Yamamoto reported very recently at the XV World Poultry Congress on a procedure for producing a broth propagated bacterin against infectious coryza which did not require concentration. Their procedure, however, requires the use of chicken serum or brain heart infusion broth to obtain the necessary concentration.
Thus, there is a need for a method of propagating Haemophilus gallinarum to provide, without the need for addition of serum or infusion broth or subsequent concentration, a product containing at least 10.sup.8 CFU/ml.